Vegetable oils when subjected to low temperature environments undergo solidification through crystallization and therefore are a major hurdle for use in industrial applications. The relatively poor low temperature flow properties of vegetable oils arise from the appearance of waxy crystals that rapidly agglomerate resulting in the solidification of the oil.
This invention relates to a method of dewaxing and degumming vegetable oils to avoid this crystallization. More particularly, the present invention is concerned with a method of removing a wax and phospholipid from a vegetable oil through processing in a multistage flow-through, hydrodynamic cavitation device.
Waxes are natural components of many vegetable oils, including sunflower oils, consisting mainly of esters of fatty acids with fatty alcohols, that are partially removed in winterization processes during oil refining. The quality and stability of vegetable oils such as sunflower oil are influenced by the presence of minor constituents such as waxes. Waxes are mainly esters of FA with fatty alcohols, having 36 to 50 carbon atoms. Waxes tend to crystallize and cause turbidity when the oil is cooled, interfering with oil processing and marketing. They are partially removed during refining in the winterization or dewaxing process, which is carried out in order to obtain completely clear oil that is not affected by low storage temperatures.
A method for purifying vegetable oils obtained by mechanical extraction is disclosed in U.S. Pat. No. 6,307,077 to Quear. The vegetable oils are cooled to induce the insoluble material to agglomerate and to form larger masses of insoluble material. The crude vegetable oil is cooled to a temperature between about 5° C. and 0° C. The vegetable oil may be maintained at this cold temperature for a minimum amount of time, preferably between about 1 hour and about 8 hours. After the vegetable oil has been cooled and stored, the oil is rapidly heated so as to induce the insoluble material to precipitate out. In a preferred embodiment, the vegetable oil is heated to temperature between about 50° C. and about 80° C.
Prior to human consumption, vegetable oil undergoes processing which generally includes bleaching, deodorization and the removal of unwanted particulate material. The unwanted particulate material includes wax, which shall mean for the purposes herein high melting glycerides such as saturated glycerides having 16 to 18 carbons. The oil dewaxing equipment is used in oil refining process for oil with high wax content as well as some salad oils. The oil needing dewaxing includes corngerm oil with a wax content typically being 0.01% to 0.04%, sunflower oil with a wax content typically from 0.06% to 0.2%, ricebran oil with a wax content typically between 1% to 5% and including olive oil and walnut oil.
Typically vegetable oil is extracted from seed, refined and bleached. After bleaching, the hot oil—usually about 120° F.—is sent to a “winterization” unit. Winterization is a process by which higher-melting glycerides are crystallized for removal from the oil. Some vegetable oils require winterization and the removal of higher melting glycerides to avoid problems in the use of the oils at lower temperatures and in later processing. Other vegetable oils do not require winterization to remain processable at lower temperatures. The cooling crystallization lasts up to 48 hours.
Dewaxing (also called winterization) is carried out by slowly chilling the oil to 7-15° C. followed by filtration of precipitated solids. The cooled oil is held in a specially insulated tank with a special slow-speed mechanical agitator. Preferably, the oil is held for 12-48 hours at this temperature.
The waxes are separated from the oils by employing crystallization techniques. After the wax is crystallized, the wax is usually separated from the oils in filter presses using pre-coated plates of diatomaceous earth.
Prior to the instant invention, it was generally assumed that during winterization for the formation of wax crystals in the oils, the temperature of the oils are lowered at a slow cooling rate to allow crystallization so that a true solid liquid separation process can be effected. It has been generally believed, however, that the oil should be cooled slowly and carefully to avoid difficulty in the filtration process. This slow cooling is not energy efficient, particularly if heating is required to control the cooling rate. Further, the slow cooling of the oil slows the production of winterized refined oil.
Therefore, it is desirable to develop a process for removing waxes and other particulate materials from oils in a more efficient and less energy intensive manner.
Removal of phospholipids from oil plays an important role not only in the quality of refined food grade oil, but also in production of lecithin. Plant lecithins are a by-product of the refining of vegetable oils. During the usual batch degumming process, the crude oil is heated to about 70° C., mixed with 2% water and subjected to thorough stirring for about half an hour to an hour. This addition of water to the oil hydrates the polar lipids in the oil, making them insoluble. The resulting lecithin is then separated by centrifugation.
The lecithin is made up of water, phospholipids and glycolipids, some triglycerides, carbohydrates, traces of sterols, free fatty acids and carotenoids. The crude plant lecithin is obtained by careful drying. The composition and quality of the crude lecithin product are considerably influenced by the quality and origin of the oilseeds, as well as the conditions during the de-gumming process.
During conventional water degumming processes only hydratable phospholipids can be removed from oil. Non-hydratable phospholipids can be removed from the oil with the addition of phosphoric or citric acid.
Food grade lecithin can be obtained only if extracted from oil by the addition of water in the water degumming process but not with phosphoric or citric acid. This process limits the quantity of food grade lecithin that can be obtained from crude oil, because only hydratable phospholipids can be removed with water. If acid is added to the oil during refining it will remove remaining non-hydratable phospholipids, but these non-hydratable phospholipids are suitable only for industrial grade lecithin production and not for a food grade lecithin.
A process for treating organic acid-treated phosphatides is disclosed in U.S. Pat. No. 6,441,209 to Copeland et al. The process for treating a phosphatide-containing material disclosed by Copeland et al. involves providing a phosphatide-containing material having a phosphatide-enriched aqueous phase obtained from an organic acid refining process, an organic acid-treated phosphatide phase obtained from an organic acid refining process, or a mixture thereof; adjusting the pH of the phosphatide-containing material; and drying the neutralized phosphatide for a time sufficient to produce a dried phosphatide containing hydrolyzed lecithin.
U.S. Pat. No. 8,232,418 to Bilbie et al. discloses a method for the preparation of lecithin and involves heating the oil to a suitable temperature, contacting the oil with a peroxide solution, separating the lecithin precipitate from the oil, and drying the lecithin.
Lecithin is recognized by the FDA as GRAS, i.e. Generally Regarded as Safe, 21 CFR, 1841400, and is used as a non-toxic surfactant, emulsifier, lubricant and to produce liposomes. Commercial lecithin is a mixture of various phospholipids, such as phosphatic acid, phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositol, depending on the source and production.
In fluid processing, it is well known that localized increases in both pressure and temperature along with vigorous mixing provided by cavitation can initiate and accelerate numerous reactions and processes. Enhancing the reaction yields and process efficiencies by means of the energy released upon the collapse of cavities generated in the fluidic media has found numerous applications. Although extreme overall pressure or heat can be disadvantageous, the outcome of an optimized cavitation treatment has proven to be beneficial.
Cavitation can be of different origins, including hydrodynamic, acoustic, ultrasonic, laser-induced and generated by injecting steam into a cooled fluid. Simultaneous application of two or more cavitation-generating techniques may provide an even better outcome, i.e., coupling steam injection cavitation with acoustic cavitation improves efficiency by 16 times (Young, 1999; Gogate, 2008; Mahulkar et al., 2008).
If fluid flow is directed in a flow-through hydrodynamic cavitation apparatus at a proper velocity, the vapor-filled bubbles will form within the flow due to the drop in fluid pressure below the vapor pressure. The bubbles collapse in a slow-velocity, high-pressure zone, causing sharp localized increases in both pressure and temperature, the formation of high-velocity streams and shock waves, vigorous shearing forces, and the release of a substantial amount of energy. This process activates atoms, molecules, ions and/or radicals located in the bubbles and the surrounding liquid, and initiates chemical reactions and processes. The bubble implosion can also result in the emission of light favoring photoreactions and radical generation.
The cavitation phenomenon is categorized by cavitation number Cv, defined as: Cv=(P−Pv)/0.5ρV2, where P is the pressure downstream of a constriction, Pv is the fluid's vapor pressure, ρ is the fluid's density, and V is the fluid's velocity at the orifice. Cavitation starts at Cv=1, and Cv<1 implies a high degree of cavitation. The number of cavitation events in a flow unit is another important parameter. (Suslick, 1989; Didenko et al., 1999; Suslick et al., 1999; Young, 1999; Gogate, 2008; Passandideh-Fard and Roohi, 2008; Zhang et al., 2008)
Distinct from acoustic cavitation, flow-through hydrodynamic cavitation does not require using a vessel. Numerous flow-through hydrodynamic apparatuses are known. See, for example, U.S. Pat. No. 6,705,396 to Ivannikov et al. and U.S. Pat. Nos. 7,338,551, 7,207,712, 6502,979, 5,971,601, 5,969,207 to Kozyuk and U.S. Pat. No. 7,762,715 to Gordon et al that disclose hydrodynamic cavitation apparatuses and their applications.
With the cost of energy and human health concerns rising rapidly, it is highly desirable to lower the level of impurities in edible oils and reduce the energy consumption of refining. The prior art techniques do not offer the most efficient method of dewaxing and degumming of vegetable oil in the shortest amount of time possible.
Therefore, a need exists for an improved method for processing vegetable oils. The inventive method and devices are desired particularly at oil refineries during harvest, when throughput is a key factor. The present invention provides such methods and devices, while producing improved product with shorter processing time and less accumulation of waste harmful to environment.
The present invention provides a method and device for generating cavitation in a flow of oil to be treated within at least one cavitation chamber, preferably in multiple consecutive cavitation chambers. This goal is achieved through the design of a cavitation device aimed at dewaxing and removal of phospholipids—a free fatty acid—from a crude vegetable oil and extracting at least 10% more of food grade lecithin.
To achieve as large a profit margin as possible it is necessary to decrease time, energy consumption and eliminate waste production of removing wax and phospholipids. The prior art methods do not offer the most efficient method in the shortest time possible. Therefore, a need exists for the improved method and device for dewaxing with a minimal residence time and energy cost that produces dewaxed oils with low levels of phospholipids. The present invention satisfies these needs and provides other related advantages.
It is an object of this invention to provide a rapid energy efficient continuous process for treating vegetable oils, which process is effective without a slow cooling of the oil, but which is economic and produces a vegetable oil that is not turbid at lower temperatures.
It is also an object of this invention to provide a process which would remove wax and phospholipids.
It is also an object to remove more phospholipids with water and a small amount of citric acid to maintain food grade lecithin production.
It is another object of this invention to reduce the time required for winterization.
It is also an object to remove hydratable and partially non-hydratable phospholipids with only water.
It is also an object to remove more phospholipids with addition of water and citric acid and maintain food grade lecithin production.
It is also an object of this invention to improve extraction of food grade lecithin by at least ten percent.
Still further objects and advantages of the invention will be found by reference to the following description.